1. Field of the Invention
The present invention relates to a method for designing the arrangement of tips of a leadframe used in a semiconductor device or the like and, more specifically, to a leadframe tip arrangement designing method which determines an optimum arrangement of leads of a leadframe.
2. Background Art
In conventional leadframe tip arrangement designing methods, as exemplified by Japanese Patent Application Laid-Open No. 7-49894, the arrangement position of a cavity line, for instance, of leadframe tips is specified and the leadframe tip width and interval are determined according to the same criterion (such as criterion pertaining to a circle diameter). Therefore, it is difficult to provide proper arrangement positions. For the same reason, it is difficult to provide optimum values independently for those parameters.
FIG. 8 shows an algorithm of a conventional leadframe tip arrangement designing method of the above-described kind. In FIG. 8, step S1-2 denotes a design condition input step for inputting design conditions such as leadframe tip arrangement lines. Step S4-2 denotes a leadframe tip width setting step for setting a leadframe tip width. Step S4-3 denotes a leadframe tip interval calculation step for determining a leadframe tip interval. Step S5-2 denotes a processing step for judging whether the leadframe tip width and interval fall within the ranges of the desired design conditions. Step S7 denotes a processing step for judging whether the leadframe tips satisfy design criteria. Finally, step S8 denotes a processing step for illustrating the design results to the user.
Referring to FIG. 8, the conventional leadframe tip position determining method will be described below in further detail. First, at step S1-2, design conditions of leadframe tip arrangement lines such as a cavity line are inputted. At step S4-2, a leadframe tip width is set by defining a leadframe width in accordance with the diameter of a circle. At step S4-3, a leadframe position (i.e. where to dispose the leadframe) is determined by determining the center coordinates of the circle. The leadframe interval is also determined. At step S5-2, it is judged whether the tip width and interval of the leadframe (that are defined by a tangential line of the circle determined at steps S4-2 and S4-3) fall outside of the desired design conditions. If the determined leadframe tips are judged to be outside of the ranges of the design conditions (YES) at step S5-2, the process returns to step S4-3, where the center of the circle which determines where to dispose the leadframe is moved to change the leadframe tip interval. If the determined leadframe tips are judged not outside of the ranges of the design conditions (NO), the process goes to step S7, where the determined leadframe tips are judged to determine whether they satisfy design criteria. If the determined leadframe tips satisfy the design criteria (YES) at step S7, design results are displayed at step S8. If the determined leadframe tips do not satisfy the design conditions (NO), the process returns to step S4-2 to reset the leadframe tip width.
The above conventional design method has a disadvantage in that a plurality of arrangement lines such as cavity lines need to be inputted as design conditions. Further, since the leadframe tip width and interval are determined according to the same criterion, pertaining to a circle diameter, for instance, it is difficult to provide optimum values independently for the leadframe tip width and interval.
As described above, in the conventional leadframe tip arrangement designing method, it is difficult to determine a cavity line where leadframe tips are located. As a result, designing takes a long time and design results vary to a large extent from one designer to another. Further, the conventional method has the disadvantage that the leadframe tip width and interval cannot be set independently because they are determined according to the same criterion. This is a significant limitation on this design method's potential and usefulness.